Surface technology

Oil-water-separation / degreasing bath treatment

Treatment of oil-water-emulsions for surface treatment (e.g. pre-treatment of metal parts for ed-paint), recovery companies (e.g. for the treatment of alkaline emulsions for part washing), and so on.

  • Separation of emulgated oil particles and recycling of the cleaned liquid into the degreasing bath
  • Concentration of oil-water-emulsions for disposal
  • Cleaning of the oil-water-mixture for indirect lead-in

Principle of this process:

Aqueous degreasing baths content a tenside combination, alkalines like soda, caustic soda, phosphate, silicate and further complex molecules. The degreasing bath is loosing its efficiency, when to oil content reaches some g / litre. External pollutions also degrease the degreasing efficiency. By ultrafiltration, the oil content can be separated from the degreasing bath and the oil will be collected in the concentrate.

The degreasing bath will be dumped into a buffer tank and then pumped in the working tank of the ultrafiltration plant. The flow is regulated by the level of the working tank. In the working tank, there is a coarse filter installed (mostly a belt filter) to retain the coarse particles. In the first part of the working tank, oil can sediment, can be skimmed and given into the waste oil storage.

The pre-cleaned emulsion is pumped into the next step of the working tank and flows into an ultrafiltration plant (feed and bleed system).

At the ultrafiltration membranes, oils, greases and fine particles are separated. Depending on the application the permeate of the ultrafiltration plant can be disposed or leaded back to the degreasing bath. Never-the-less some chemicals for the degreasing process have to added again, because they have also been separated by ultrafiltration.

The concentrate is treated again, to concentrate the oil as much as possible. With increasing oil concentration, the filtration flow degreases. So, if the concentrate flow falls below a boundary value, the process will be stopped and the concentration will be dumped.

Before running a new batch, the concentrate has to be removed from the pipe-work. After that, the next batch of oily emulsion can be treated.

With ultrafiltration, the oil content can be increased up to 25-35%.

The ultrafiltration plant is running at the cross-flow principle with a close pore size.

Before dumping the permeate, the local authorities have to be consultated, because the regulation for waste water disposal are very different all over Germany and Europe.


  • Treatment of oil-water-emulsions is possible and established
  • High retention rates (oil, KW,COD, and so on)
  • Recycling of the process water and permeate is possible and established
  • Constant oil concentration of the degreasing bath means constant production conditions
  • Reduction of the waste water amount
  • Compact and modular design
  • Fully-automized means low operation costs

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